Salty, sweet, sour and bitter have been recognized as the four pillars of taste for centuries. All other tastes were thought to come from a combination of these flavors. But what’s the word for the savory roof-of-the-mouth sensation of parmesan cheese, beefsteak tomatoes, and seaweed? Borrowed from a combination of the Japanese words umai- (delicious) and mi (taste), umami describes the protein-based flavor of glutamates.

In 1908, Japanese chemist Kikunae Ikeda identified glutamic acid as the source of the distinct flavor of kombu seaweed. Glutamates, the salts of glutamic acid, are naturally present in most living things. When organic matter breaks down, such as when kelp is cooked in a broth, glutamate molecules break apart and become L-glutamate. It’s the same when you ferment cheese or cook meat, processes that remove moisture and condense glutamates. L-glutamate is the tastant that gave Ikeda’s kelp broth its distinct flavor. He called it umami.

Ikeda experimented with isolating different glutamates and discovered that monosodium glutamate was the most palatable. Although his idea of umami as a distinct fifth flavor was not well-received at the time, Ikeda proceeded with a production patent for MSG. Ajinomoto started manufacturing the crystallized flavor enhancer in 1909.

MSG was recognized in the US as a safe food additive in 1959 because it had a history of safe use, and there were no current studies of its side effects. Then in 1968, the term “Chinese-Restaurant Syndrome” was coined to describe the numbness, weakness and palpitations some people get in response to MSG. This created a stigma that had consumers looking to avoid it while manufacturers looked for ways to present “clean labels” on the shelves. “No MSG Added” became a label favorite, even if the ingredients included other glutamate flavor enhancers that did not have to be labeled as such.

The stigma persists, and mixed study results continue to fuel the debate on MSG’s side effects and excitotoxicity.

Despite the nasty reputation of MSG, umami came to be recognized as the fifth flavor in 2002 when scientists found a special receptor for L-glutamate; It was thought to have evolved as a way to test food for protein content. People have been cooking for savory glutamate flavor since ancient times, but the discovery of the receptor kicked off an umami trend that had restaurants serving foods that are natural “glutamate bombs” like anchovies, cured meats and aged cheeses. Food manufacturers have also started using MSG-like artificial ingredients like Senomyx to play off the receptor and make their products so that you “can’t eat just one.” Next time you see a “natural” snack food with hydrolised anything in the ingredients, it’s likely the manufacturers’ take on “clean label” umami.